Curable silicone compositions that contain a resin-form organopolysiloxane and that provide a highly transparent cured silicone material are known. For example, JP 2005-042099 (Equivalent to US 2005-0006794 A1) A describes a silicone rubber composition comprising an organopolysiloxane that has at least two aliphatically unsaturated bonds in each molecule; an organopolysiloxane having a resin structure and comprising the SiO2 unit, an R3SiO0.5 unit having 2-3 vinyl groups, and an R3SiO0.5 unit having 0-1 vinyl group, wherein the non-vinyl R in these formulas is monovalent hydrocarbyl that does not contain an aliphatically unsaturated bond, e.g., methyl and so forth; an organohydrogenpolysiloxane that has at least two silicon-bonded hydrogen atoms in each molecule; and a platinum group metal-based catalyst. In the following, the SiO2 unit is referred to as the Q unit and the R3SiO0.5 unit is referred to as the M unit.
The polyorganosiloxane composition described in JP 2006-335857 A provides a transparent cured material and comprises a straight-chain polyorganosiloxane containing silicon-bonded alkenyl and having a viscosity at 23° C. of 10 to 10,000 mm2/s; a branched polyorganosiloxane comprising the Q unit, an M unit having one vinyl group, and an M unit that does not contain an aliphatically unsaturated bond; a polyalkylhydrogensiloxane comprising the Q unit, an M unit having one silicon-bonded hydrogen atom, and an M unit that does not contain silicon-bonded hydrogen; and a platinum group metal compound.
The curable silicone composition described in JP 2007-131694 A (equivalent to US2009-0118441 A1) comprises at least a diorganopolysiloxane that has at least two alkenyl groups in each molecule; at least two resin-form organopolysiloxanes that have different mass-average molecular weights, each comprising the Q unit, an M unit having one vinyl group, and an M unit that does not contain an aliphatically unsaturated bond; an organopolysiloxane that has at least two silicon-bonded hydrogen atoms in each molecule; and a hydrosilylation reaction catalyst.
JP 2006-328102 A (equivalent to US2006-0264583 A1) describes a silicone polymer composition for lens molding, that characteristically provides a colorless and transparent cured material and that comprises as its essential components an organopolysiloxane that has at least two aliphatically unsaturated bonds in each molecule and a viscosity of at least 100 mPa·s at 25° C., an organohydrogenpolysiloxane that has at least three H(CH3)2SiO1/2 units in each molecule, and a platinum group metal catalyst.
However, the cured silicone materials provided by the cure of such compositions have a poor flexibility and are prone to breakage during mold-based molding and during component assembly processes, and it has also not been possible to use them in applications that demand bendability due to use in a flexed or bent condition. In addition, the cured silicone materials provided by the cure of these compositions are subject to temperature-induced changes in transparency, and problems due to optical property variations are then produced when these cured silicone materials are used over a broad temperature range.